(a) Field of the Invention
The present invention is related to a growing method of a SiC single crystal, and in particular, to a growing method of a high quality SiC single crystal that has only small amounts of defects.
(b) Description of the Related Art
Broadband semiconductor materials, such as SiC, GaN, AIN, and ZnO, have been noticed as promising next generation semiconductor device materials.
However, since the growth technology of a single crystal ingot is not secured, only SiC single crystal material can be used in a substrate having a diameter of 2 inches or greater among these broadband semiconductor materials.
SiC has excellent thermal stability at 1500° C. or less and also has excellent stability in an oxidizing atmosphere. It also has a high thermal conductivity of 4.6 W/cm° C.
Thus, in the case that high stability at high temperature for a long time is required, SiC promises to be much more useful than III-V group compound semiconductors, such as GaAs or GaN.
Though the electron mobility of SiC is lower than that of Si, it has a band gap two or three times as much as Si.
Thus, SiC has a much higher operation limit temperature than Si. In addition, since it has high chemical stability and high mechanical strength, it can be used in a device that can be used in extreme environmental conditions.
The performance limitation of a device caused by the difference of intrinsic properties of these materials can be expressed by a FOM (Figure of Merit) such as JFOM (Johnson's Figure of Merit), KFOM (Keyes' Figure of Merit), BFOM (Baliga's Figure of Merit) and BHFFOM (Baliga's High Frequency Figure of Merit) easily.
JFOM is an indicator of high frequency performance of a material. JFOM is a comparative coefficient of a power of a transistor and a limit of a frequency induced from a break down voltage and a saturation electronic speed. JFOM of SiC is 600 times or greater than that of Si.
Devices developed by using SiC having such excellent properties are announced day by day. Accordingly, the scope of application of SiC is becoming very wide and its ripple effect is being enlarged at very fast pace.
As to the applications of high frequency devices for communication, a single crystal substrate having high resistivity (103 ohm-cm or greater) is required.
For this application, a high quality substrate having only small amounts of defects is required.
The high quality substrate generally indicates a substrate in which the number of micro pipes per unit area and the dislocation per unit area generated in a SiC single crystal are small.
Moreover, the generation of defects is very closely related to the SiC source, purity of the crucible material, and fine dust.
Among these, the SiC source used in the growth has a large influence on the generation of the defects. Particularly, even if a high purity SiC source is used in the growth, the defects may be generated due to the residual metallic Si not reacted with a carbon in the high SiC purity source.
In addition, in order to be adapted to high brightness and high power type LEDs (light emitting diodes) and LDs (Laser Diodes), and a power device, the SiC substrate should be a low resistance substrate that can embody a vertical type diode structure.
A high quality substrate in which the stacking defect and the other crystal defects are minimized is required for these applications.
Nitrogen is generally used as a doping source in order to embody an n-type impurity in the SiC single crystal growth. If the nitrogen is intentionally over-added in order to increase the doping concentration, the defects, including the stacking defect that is fatal to the characteristics of a device, may be generated.